1. Field of the Invention
The present invention relates generally to self-propelled devices capable of raising, lowering, and transporting heavy elongated objects. More particularly, the present invention relates to a self-propelled heat exchanger tube bundle extractor that is capable of removing a heat exchanger tube bundle from an elevated horizontally disposed heat exchanger shell and transporting the tube bundle to another location for maintenance.
A great variety of chemical processing plants utilize large cylindrical heat exchangers. The heat exchangers typically comprise a horizontally disposed cylindrical shell containing a cylindrical tube bundle which is composed of a number of parallel metal tubes. The tube bundles themselves maybe very large, up to 60 ft. in length and weighing up to 100 tons or more.
A heat exchanger channel ordinarily is coupled to the front of each heat exchanger shell. The channel is double flange section of pipe having an inlet and outlet to enable fluid to pass into the heat exchanger tubes, pass through the tube bundle tubes, and exit out the channel either, at a lower or higher temperature, as the case may be.
Large heat exchangers, while having a potential life span of several years, will normally require maintenance at some point in time. Performing maintenance on a large cylindrical heat exchanger normally entails removing the tube bundle and transporting it to another location for maintenance. The down time associated with removing and replacing the heat exchanger tube bundle may represent an added cost of operation to the facility. It is therefore desirable to be able to remove and replace the heat exchanger tube bundle as quickly as possible, and as safely as possible.
The problem of plant down time as a result of tube bundle replacement is exacerbated in situations where two or more heat exchanger shells are stacked on top of one another. If the top tube bundle in such a stacked arrangement requires maintenance, it will be necessary to either dismantle the lower heat exchanger channels in order to reach the top heat exchanger bundle, or to utilize a lifting apparatus that is capable of avoiding the lower heat exchanger channels. If the lower most heat exchanger channel must be removed to be able to position the lifting apparatus next to the heat exchanger bundle that is to be extracted, several heat exchangers at once will be taken off line, resulting in a much higher down time cost for maintenance.
Some chemical plants place further constraints on the removal of heat exchanger tube bundles. For example, in some circumstances, the arrangement of piping at or near the heat exchanger shell may provide very little room to maneuver an apparatus in position to remove the failing tube bundle. In such applications, it is desirable to have an extractor apparatus that is not only self-propelled, but able to make fine tuned adjustments along either an X, Y or Z axis in order to avoid any obstacles presented by the plant hardware and to be able to more quickly and accurately align the tube bundle.
2. Brief Description of the Prior Art
The prior art contains a number of self-propelled heat exchanger tube bundle extractors such as Cradeur, U.S. Pat. No. 4,666,365, Krajicek, U.S. Pat. No. 4,575,305, Bauch, U.S. Pat. No. 4,392,524, Boisture, U.S. Pat. No. 5,169,281.
These devices typically utilize a risible boom or telescoping column mounted on a vehicle chassis of some sort. These devices, while providing a self-propelled capability, have the disadvantage of introducing cantilevered forces on the lifting system which introduce instability into the system when the tube bundle is lifted out of the tube shell. Even providing large counterweights on the vehicle chassis to counteract the moments introduced by the offset between the center of gravity of the tube bundle and the lifting boom or telescoping column may not be sufficient to successfully overcome the moments.
Another set of prior art devices utilizes a wheel mounted frame work that is wheeled into position adjacent the tube bundle. When the desired position is reached, the entire frame work is elevated on a series of outriggers either by hydraulic means or by chains and pulleys. These devices, for example, the American Mechanical Services, Inc., Model SP-A-101 and the M&H Manufacturing Corporation's bundle wagon do not suffer from the same cantilever force problems that the earlier mentioned systems do, however, they too have inherent disadvantages. For example, the bundle wagon is not self-propelled, and thus requires a separate vehicle for transport and positioning. Furthermore, both the bundle wagon and the SP-A-101, once positioned, and elevated, i.e., along a Z-axis, cannot be translated along either an X or Y axis. Consequently, if it turns out that such systems must be adjusted in either an X or Y direction after the units have been elevated, the units must then be lowered back to ground level, repositioned, and then raised again.
The present invention is directed to overcoming one or more of the aforementioned disadvantages.
In one aspect of the present invention, a lifter for transporting an elongated object over a surface comprises an elongated main frame that has at least two lifting columns that are vertically disposed in spaced apart relation. At least four wheels are pivotally coupled to the main frame. The wheels are controllably operable to propel and steer the lifter and to remain in contact with the surface. An extraction frame is coupled to the lifting columns and is controllably movable with respect to the main frame along a first predetermined path, a second predetermined path, and a third predetermined path. A pulling device is controllably movable along a fourth predetermined path parallel to the first predetermined path to selectively pull the object on to and push the object off of the extraction frame.
In another aspect of the present invention, a lifter for transporting an elongated object over a surface comprises an elongated main frame that has a pair of parallel beams that extend generally parallel to an X-axis. At least one cross member is coupled to the beams and extends generally parallel to a Y-axis. At least two parallel lifting columns are coupled to the beams and extend generally parallel to a Z-axis. At least four wheels are pivotally coupled to the main frame. The wheels are controllably operable to pivot 360.degree. and to translate the lifter and to remain in contact with the surface. An extraction frame is slidably coupled to the lifting columns to permit translation of the extraction frame parallel to the Z-axis. The extraction frame has first and second parallel members that extend generally parallel to the X-axis. In addition, the extraction frame has a plurality of parallel spars that are disposed on the extraction frame and that extend generally parallel to the Y-axis. The parallel members are controllably movable parallel to the Y-axis and controllably movable to the X-axis. A pulling car is slidably mounted on the parallel members of the extraction frame. The pulling car has an interior and is controllably movable parallel to the X-axis to selectively pull the object on to and push the object off of the extraction frame. A lifting mechanism is coupled to the main frame. The lifting mechanism is controllably operable to translate the extraction frame parallel to the Z-axis. A drive mechanism that has a drive shaft is coupled to the pulling car and to the extraction frame. The drive mechanism is controllably operable to translate the pulling car parallel to the X-axis. A first translating mechanism is coupled to the extraction frame. The first translating mechanism is operable to translate the parallel members parallel to the Y-axis. A second translating mechanism is coupled to the extraction frame. The second translating mechanism is operable to translate the parallel members parallel to the X-axis.